1. Field of the Invention
The present invention relates generally to reinforcement fibers for use in composites and more particularly for sizing materials for reinforcing fibers in composites.
2. Description of the Background Art
Sizing materials are commonly used in reinforced composites to assure strong bonding between a reinforcing fiber (made of carbon or other suitable material) and the polymeric matrix material which holds the fibers in a particular configuration. For a reinforced composite material to have good high temperature strength, it is not sufficient for only the matrix and the reinforcing fibers to resist thermal decomposition. If sized fibers are being used, the sizing for the reinforcing fibers must also be resistant to thermal decomposition at high temperatures.
Current sizing materials, for example, epoxies and polyvinyl alcohol, cannot withstand the temperatures to which advanced high temperature composite materials are exposed. Thus, a polymeric composite may fail, on exposure to elevated temperatures, at the interface between the polymer matrix material and fibers sized with these materials, resulting in a reduction of mechanical properties. The failure or reduction in composite properties could be attributed to the decomposition of the sizing material at elevated temperatures, either in use or during a high temperature cure. DuPont attempted to develop a high temperature sizing material from highly aromatic thermoplastic polyimides, but was unsuccessful.